Sometimes communicating by voice in areas subject to noise influences is not only problematical, but is even often impossible. To begin with, the speaker might be able to be heard by raising his voice, but after a short while, due to the vocal chords tiring, he will regularly switch over to communication by means of gesticulation, with all the disadvantages associated therewith, both at the speaker who can no longer communicate everything and at the hearer who will seldom understand much of it. Difficulty in communication may, depending on the location, have catastrophic results, either because economic damage can result or because, which would then be far worse, people could be endangered as a result. In addition, there are activities in our society where perfect communication under difficult conditions constitutes a mandatory requirement: these include, for example, communication between pilots and ground control, communication in and out of engine rooms, emergency operations in a noisy environment etc.